In cellular communications, a user equipment (UE) existing in a cell accesses a base station, receives control information for exchange of data from a base station, and then transceives data with the base station in order to perform communication. In particular, the UE transceives data through the base station, and accordingly in order for the UE to transmit data to another cellular UE, the UE transmits its data to the base station and the base station in turn transmits the received data to another UE. Since UEs can only transmit data to another UE via the base station, the base station performs scheduling of channels and resources for data transmission and reception and transmits the information about the channel and resource scheduling to each UE. Thus, in order to perform UE-to-UE communication via the base station, each UE needs to have channel and resource allocations for data transmission and reception from the base station. In device-to-device communication, on the other hand, one UE directly transmits and receives signals with another UE to which the UE intends to transmit data, without using a base station or a relay node.